Automatic tank pump down



Sept. 15, 1, 53 R CYR 2,652,188 AUTOMATIC TANK PUMP DOWN Filed July 8,1948 4 Sheets-Sheet 1 INVENTOR. Eob RoyC'yr 1 :15.4.

Sept. 15, 1953 V R. R. CYR 2,652,188

AUTOMATIC TANK PUMP DOWN Filed July 8, 194a 4 SheetSSheet 2 INVENTORQAob Pay cfyr' v Sept. 15, 1953 R. R. CYR

AUTOMATIC TANK PUMP DOWN 4 Sheets-Shet 5 Filed July 8, 1948 P/ran/ P0wer Okra/Z k L 0&2 P6: We: Oez

T0 lnckout Relay fi i 56 uence C/fcu/z awe/mm Rob Fay C30 Sept. 15, 1953R. R. CYR 2,652,188

AUTOMATIC TANK PUMP DOWN Filed July 8, 1948 4 Sheets-Sheet 4 'Pob RoyCyr Q EL 3 Til jg.

Patented Sept. 15, 1953 AUTOMATIC TANK PUMP DOWN Rob Roy Cyr, Berkeley,Calif., assignor, by mesne assignments, to the United States of Americaas represented by the United States Atomic Energy Commission ApplicationJuly 8, 1948, Serial No. 37,681

8 Claims.

My invention relates to vacuum systems, and more particularly to asystem for automatically controlling the sequence of operations of aseries of pumps for creating a vacuum.

The procedure involved in pumping down a tank or vacuum system in thepast has been a manually controlled rather than an automatic procedure.In view of the low pressures required for certain processes, amechanical pump is not suitable for that function. On the other hand,dlifusion pumps capable of exhausting to low pressures will not operateagainst air pressure. Accordingly, it has been necessary to provide avacuum system wherein both mechanical and diffusion pumps are arrangedto work together. In this arrangement one or more diffusion pumps isconnected to the tank or chamber to be exhausted, through gate valves.The outputs of the diffusion pumps are preferably tied together and fedthrough a finishing valve to the input of amechanical pump so that thediffusion pumps may work into a pressure lower than atmosphericpressure. Either an additional mechanical pump may be provided forpartially evacuating or making the initial evacuation of the tank orchamber, or a by-pass line may be provided so that by the use of aroughing valve, a single mechanical pump may be employed for roughingdown purposes and for cooperation with the diffusion pumps in exhaustingthe tank or vacuum system to a low vacuum.

The actuation of these valves has been accomplish-ed manually or throughmanual control. Under usual operating conditions the equipment inquestion is large and bulky. Pumps, tanks, and valves are ordinarilyseparated by considerable distances and may be located in differentrooms or even different floors of a building. Intercommunication systemsand several operators may be required to manually operate the controlsin. their proper sequence. When meters are at some distance from thevalves, and a single operator is employed to take care of the manualcontrols, it requires a great deal of moving about from place to placewhere the different controls and meters are located. Further, manualcontrols are slower, and require continual watchin of the gauges, andmistakes are quite often made in the manipulation of the valves or inthe operation of the system. These mistakes are in some instances quitecostly, causing damage not only to process materials but to the pumpingfluids.

Applicant with a knowledge of all of these defects in and objections tothe prior art has for an object of his invention the provision of asystem for automatically pumping down a tank or reservoir to high vacuumby a sequence of operations.

Applicant has as another object of his invention the provision of anelectrical control circuit for controlling the operation of a series ofpumps in the proper sequence to pump down a tank or reservoir to highvacuum, or to evacuate a chamber.

Applicant has as a further object of his invention the provision of anelectrical control circuit for automatically controlling the pumpingdown of a tank or reservoir to a high vacuum so that upon closing thecircuit, the finishing valve, the roughing valve, and the main gatevalves, which regulate the operation of a series of pumps, are made toopen and close in a predetermined sequence.

Applicant has as a further object of his invention the provision of anelectric circuit control for automatically associating mechanical anddiffusion pumps in a certain predetermined sequence to pump a tank,reservoir, or chamber to high vacuum.

Other objects and advantages of my invention will appear from thefollowing specification and agcompanying drawings, and the novelfeatures thereof will be particularly pointed out in the annexed claims.

In the drawings, Fig. l is a fragmental detail of a torque limitingswitch, used on the valve operator in my improved system. Fig. 2 is aschematic of the pumping arrangement employed in connection with myimproved system. Fig. 3 is a perspective of a gear limiting switch. usedon valves in my improved vacuum system. Fig. 4 is a diagram indicatingthe sequence of operation of the various valves and pumps shown in Fig.2. Fig. 5 is a schematic of the hot wire gauge used in myimprovedsystem. Fig. 6 is a detail showing the relation of the segmentsused in the hot wire gauge. Fig. '7 is a schematic of the circuits knownas the Pirani power supply circuit or Pirani power circuit and thePirani signal circuit. Fig. 8 is a schematic of the sequence circuit.Fig. 9 is a schematic of the control circuit. Fig. 10 is aschematic ofthe valve power circuit.

The procedure involved in pumping down a tank in the past has been amanual rather than an automatic procedure, the sequence involved beingthat as shown in the flow diagram of Fig. 4 of the drawings. Briefly theautomatic sequence is as follows: A manual push button is pressed whichcauses the finishing valve to close, the finishing valve being in openposition when the tank is down to air; next the roughing valve opens,and when it opens the pressure at the Pirani gauge will be at or willrise to a value above 100 microns; when it falls to a value below 100microns the roughing valve closes and then the finishing valve opens;when the finishing valve opens, the air from within the diffusion pumpswill again cause the pressure at the Pirani gauge to rise above 100microns; when the pressure again falls below 100 microns, the mechan calpump being in operation, of course, the mam gate valve will open, asindicated by the chart of Fig. 4.

The arrangement of the pumps and valves and their connections are asshown in the drawings, each element being identified by legend. It willbe noted from Fig. 2 that the roughing valve 23 is in a by-pass lineextending around the main gate valves 24, 25, the diffusion pumps I9, 20and the finishing valve 28.

In this system it is contemplated that the roughing, finishing and gatevalves will be electrically actuated. The valve operators used inconnection with this system are preferably of the motor driven type suchas those manufactured by the Philadelphia Gear Works of Philadelphia,Pennsylvania and sold under the name of- Limitorque. While theparticular structure of these operators constitutes no part ofapplicants invention, one form thereof is disclosed in Fig. l in ordertogive a better understanding of the system as a whole. In that figure amotor I, coupled to an appropriate power source, is directly connectedthrough its shaft 2 by a flanged coupling to a splined shaft 3 carryinga worm 4 which floats thereon and is free to move longitudinallythereof. The shaft 3 is rotatably mounted in bearings 5, 6 and thecoiled torque springs I, 8 are interposed between the ends of worm 4 andthe bearings 5, 6 and are disposed about shaft 3 in order to limit axialmovement of worm 4. The worm 4 drives a worm gear Wheel 9 mounteddirectly on stem or shaft III which by rotation opens and closes thevalve (not shown). Formed in worm 4 adjacent one end thereof is acircumferential groove II which is adapted to seat in an appropriateslot in pivoted arm I2 and is interlockingly engaged therewith. Arm I2is pivotally mounted at its lower end on bracket I3, and its upper endwhich is angularly bent is recess seated in shaft I4, slidably mountedin standards I5, I5. Engaged at opposite ends of shaft I4 are limitingswitches such as A and E, and interposed between the limiting switchesand their corresponding standards I5, I are compression springs l1, l7.Operation of motor I rotates shaft 2 and in turn shaft 3, carrying worm4. The rotation of shaft 3, depending upon the direction of the rotationof motor I, rotates worm gear 4 in a clockwise or counterclockwisedirection, turning gear wheel 9 and shaft III, to open or close thevalve, as the case may be. When the valve stem has reached the limit ofits travel, either in the closed or open position, worm gear wheel 9stops rotating, and as motor I continues its rotation, worm 4 is forcedto move longitudinally along shaft 3 compressing spring 1 or spring 8depending upon the direction of rotation of motor I. Worm 4 carriespivoted arm I2 with the sliding shaft I4 in standards I5, I5 until theshaft actuates one or other of the limiting switches A or E opening themotor circuit and stopping the motor either directly or throughappropriate control circuits.

It may be pointed out that the main gate valves referred to hereinafteremploy both torque and gear limiting switches. The gear limiting switchis preferably of the type manufactured by the Philadelphia Gear Works. Asuitable type is shown in Fig. 3 of the drawings wherein a motoroperated gear 32 actuates a train of gears 33, 34, 35, 36, 31, 38, and39 connected after the fashion of speedometer gearing, to rotate member40 carrying transversely extending contact 43 which bridges springcontacts M, 42 suspended from terminals mounted on the frame, when inclosed position. In this way many revolutions of gear 32 are required torotate the insulated member 40 a single revolution. No detaileddescription of these elements and their operation is given, however,since they constitute no part of this invention but are well known inthe prior art.

In one preferred form of the system, the main gate valves may be large20 inch valves, and operators may be of the type described above. Thefinishing and roughing valves may be of the 6 inch type and may beoperated by what are known as Pee Wee operators. These operators are ofthe same general type as those described above. The valves arepreferably of the double seating type, i. e. the valve seats in bothdirections of movement of the stem. The operators for the small valveshave torque limit switches operable on movement of the valve stems inboth directions. The motors driving these valves are preferably of thethree phase type and may be reversed to open and close them by reversingtwo of the three power leads as will appear from the connections of thetwo sets of switch contacts employed to operate the motors for thesevalves.

Referring to Fig. 2 ShOWiIlga layout of the tank, pumps, and valves, IBdesignates a tank or reservoir to be evacuated. Difiusion pumps I9, 25are connected in series with mechanical pump 2i. The mechanical pump 2|is directly connected to the tank I8 through a by-pass line 22 having aroughing valve 23 therein. Gate valves 24, 25 are interposed in lines26, 21 between diffusion pumps I9, 20 and reservoir tank I8, and afinishing valve 28 is interposed in line 29. be-

tween the diffusion pumps and mechanical pump.

A Pirani gauge 30 is connected into the system through line 3 I.

In operation, the finishing valve 28 and gate valves 24, 25 are closedand the roughing valve 23 is open. This permits the mechanical pump 2|to exhaust the tank I8 through the by-pass line 22 until the Piranigauge 30 indicates a pressure of less than microns, approximately thelowest value which can be obtained by the mechanical pump. At this pointthe roughing valve 23 closes and the finishing valve 28 opens therebycausing the pressure of the Pirani gauge 30 to rise, temporarily, due togas or air in the diffusion pumps and/or leaks in the system.Thereafter, the pressure of the Pirani gauge 30 again drops to a valuebelow 100 microns at which point the gate valves 24, 25 open and thediffusion pumps I9, 20 and mechanical pump 2| function in series toevacuate the tank to a very low pressure.

For convenience in following the sequence of operation of the variouscircuits and the relays in Figs. 7-10, inclusive, letters have usuallybeen employed for the main elements. Capital letters have generally beenemployed to designate re-- lays. Where these capital letters also havebeen followed by a small letter, the legend refers to a sub-element,such as a particular armature of a relay, since relays may have a numberof armatures. In order to aid, in locating a particular element or it su-element, the circui disclosed a be n vided i to live cate o i n mely,the Pirani power circuit, the Pirani signal circuit the Sequencecircuit, the Control circuit, and the Vol o Po er ci u t I th se figuthe r fere e t s of ea h lement, where such desi n tion used, will beIollowed with a sufiix numo al of 1, i 3 4, or respe t v ind catin inthe order enumerated above the circuit in which the el ents is ocate ThePirani power supply circuit, used to control various operations andtheir sequences, will first be considered and it will be noted that thiscircult is conventional in the art, However, it will e r e e to br eflyi rder to i a clear nderstanding of the relation it bears to the variousother circuits described in detail hereinafter. T e p s espo iveelements 61. 58 of the sual Pirani gauge are exposed to pressure in thesystem and comprise a part of the gauge 30,. To gether with resistanceelements 69, '10 they form the four legs of a Wheatstone bridge. Poweris supplied from a power source 18 through a power transformer H andconventional rectifier arrangement 12. The rectifier feeds into one setf opposite c rne s o the h a t ne bridge While the oth r set il ppositer ers a e c nnected tothe indicator or meter 80.

Th nbalance of t e br ge result f m a cha ce n resis an o resistors61,68 esp s to a chang i p e sur in t sy t m. i refle t d y t e mete 8whose arm 5 in Fi s. 5 and 6-, mov s. a r ss sector 81 t n ns to han ingre sure cond t ns.

in the meter of the Pirani system the arm 57, which swings about a pivot58, carries a contact 9 whi h pa ses ad cent t secto til ii and betweenthem and a third sector 52 which is fixedly m unted and ubst nti llycoextensive with hem The s ctors 60 and E a e preferably arri d y an rmhr ugh a ake ite or other ulatins strip to insulat t m fr m each therand ar pivo a ly mount dat 53 t u t m- An extension 64 carried by thelower end of the arm and ppropr atel supp rt d nga i h a rotating cam55, preferably driven at a uniform rate. As cam 85 rotates, sector Gilor 51 is brought into engagement with contact 59 and presses it ainst.sector 62 comp ting the circu t indicated hereinaftor. Whether it, issector 60 or 5| depends pon the pos t ono the need e or a m 1 withrespect to those sectors. However, no claim is made to any invention inthe construction of the meter. It may be the usual Allis-Chalmers Hotwire gauge which has been slightly modified by re-arranging the sectorsas indicated above. The general mode of operation or" that conven tionalgauge has not been changed, and the expianation herein is merely for thepurpose of difiGlQSiIig its function in this system.

The Pirani ge meter fin is norm lly in the position between 0 and 100microns, thus the contact 59 of the meter makes periodic engage,- mentWith sector 62 as the moving sector til acts upon it.

When contact 59 bridges sectors GI and 62, relay L2 is energized throughnormally closed contacts R3112 loadin to A. C. power source 18, andseals itself in through contacts Lag. The energizing or relay Lz closescontactLbz and complates the circuit. through relay Q2 referred to heoineiten Th s closes contact bz which o mpletes the circuit through thelock out relay in the hig ltage cubi le (not shown) which furnishespower tothe equipment to be used in connection with the evacuated tankor chamber when it has been prepared. Contacts Obi, when closed, allowthe high voltage cubicle control circuits to be energized. Naturally itis not do! sirable for these contacts to be closed when the tank isbeing rougheddown. However, the prime purpose of this feature is tode-energize the high voltage cubicle if and when a failure inthe vac.uum system causes the pressure in the system to rise above microns aspressures of this'magnitude will allow discharges in the tank which maydamage equipment in the tank as well as equip-. ment in the high\voltage cubicle. Normally closed contacts 082 are opened extinguishingthe red light BI and de-energizing relay SS2. When SS2 is deeenergized,contacts SSa'zreturn to closed position completing the circuit throughwinding of relay EH2 to sector of the meter.

This feature is peculiar to this particularapplication and might not benecessary in other processes.

When the pressure rises above 100 microns, such as by the opening of theroughing valve, contact 59 moves opposite sector 60, and it periodically completes contact between that sector and sector 62 energizingthe winding of relay BB2. Contacts RRaz are opened deeenergizing thewinding of relay L2 and the relay in the high voltage cubicle, due tothe opening of contacts Lbz and the de-energizing of relay 02 which.opens contacts 052. Contacts RRbz close completing the circuit throughQQz and through push button contacts .66. Relay QQz then seals itself inthrough contacts QQaz. It also closes QQbzrinm ing the bell 82 if thecontacts Ggz are closed. Since the winding G4 is in the circuitcontrolled by main gate valve contacts MMhl, the normally closedcontacts Ggz are closed only when the main gate valves 24, 25 are open.Since winding 02 is die-energized, contacts 062 are closed which comapletes the circuit to and lights the red light at through the powertransformer, and also ener-l gizes relay winding SS2. When winding SS2is 5 energized, normally closed contacts SSaa are opened breaking thecircuit through the winding of relay RRz. This is done to preventsegments 60 and 62 and finger 59 from periodically making andbreakingthe circuit to coil RR: which will result in damage to the contactsurfaces from arcing. If it is desired to silence the bell 82, pushbutton 66 may be depressed de-energizingrelay QQz and opening thecontacts QQbz which complete the power circuit to bell 82.

Preliminary steps In the sequence of operations detailed herein-f HHb5,and HHca in the power circuit of the driving motor 4 2 for gate valve 24as well as closing contacts HHdd to provide a locking in circuit. RelayII4 closes the power circuit to the driving motor 45 for valve 25 byclosing contacts Has,

11b5, H05 and completes a holding circuit. by closing contacts IId/l.When the valves are closed, the contacts MMcl, Mar, respectively, oftorque limit switches thereon open breaking the circuits through windins of relays EH4 and IIarespectively, and opening contacts HHa5, HHbs,HI-Ics} and Has, 11b5, 1105, respectively, in the power circuits to thedriving motors 44, 45 for gate valves 24 and 25. Contacts HHd4 and IId4also open breaking the locking in circuits for the windings of relaysHHi, I14. In addition the action of the torque limit switches permitscontacts M174 and MMZM to close completing a circuit through the windingof relay G4 energizing it and changing the positions of many contacts tobe referred to hereinafter.

To start the roughing down sequence, the push button 13 in the sequencecircuit is depressed closing its contacts. This energizes the coil ofrelay J3 which closes contacts 11414 in the control circuit to controlthe closing of the finishing valve 28, in Fig. 2, and contacts Jbs inthe sequence circuit. Closing of contacts Jos completes the circuitenergizing coil of relay K3 through push button 56 and contacts Gbs,which are maintained in closed position by winding of relay G4 which isnormally energized through contacts Mb4 and MMbi, since the lattercontacts are closed when the main gate valves 24, 25 are in closedposition. These contacts are a part of the switches controlled by themain gate valves 24, 25 and open and close with them. When the coil ofrelay K3 is energized, it seals itself in through the closing ofarmature contacts K113 and also closes contacts K173 which energizes thesequence circuit.

Normally closed contacts K04 in the control circuit are openedde-energizing coil of relay N4. This opens contacts Nai, Nba, N04, NCZ4,N64, and Nfi. It will be noted that these contacts are in the variouscontrol circuits for motors 44, 45, 46 and 41 which open and close gatevalves 24, 25, finishing valve 28, and roughing valve 23, respectively,except in the closing circuits for the motors 44, 45 of gate valves 24and 25. The action of these relays is to prevent operation of the valvesby the accidental closing of their control circuits with the manuallyoperated push buttons 48, 50, 52, 53, 54, and 55. As indicated, thecircuits of switches 49, 5| are not broken at this point, since thecircuits control the closing of main gate valves 24, 25 by motors 44,45. As these valves are already closed, no false operation can beinitiated through push buttons 49, 51, and a protective relay for eachof those circuits would not be necessary.

The energizing of the sequence circuit energizes the winding of timingrelay 2%, sequence starting pilot light 83, and buzzer transformer 81 toprovide energy for the buzzer alarm 84 when breakdown or other troubledevelops in the system. Timing relay X3 is set to close contacts Xas atthe end of a predetermined time, such as 20 minutes, in order to givethe system an opportunity to complete its cycle in the normal course ofevents and to alter the condition of the relay circuit prior to the timeof lighting the lamp or giving an alarm. Closing of contacts Xaaenergizes relay Z3 and trouble light 85 through contacts G03 and stepdown transformer 86 to indicate that the main gate valves 24, 25 areclosed. It will be remembered that winding G4 is energized through acircuit including contacts Mb. and MMb4 which are closed when main gatevalves 24, 25 are closed. The energizing of relay Z3 closes contactsZ113 operating buzzer 84 from the transformer 81, indicating that thecycle of operations has not been completed within the requisite time, i.e. that the main gate valves have not opened, that trouble of some kindexists within the system, and that proper vacuum level has not beenreached.

8 Closing finishing valve The first step in the evacuating operations isthe closing of the finishing valve 28. As previously indicated, theclosing of switch 13 in the sequence circuit energizes relay coil J3which in turn closes contacts Jim in the control circuit and starts theclosing of the finishing valve. This is accomplished by completing acircuit which energizes relay F4 through contacts Gfr, which arenormally closed when gate valves 24, 25 are closed since relay G4 isenergized through closed contacts M124 and MMbl, and through thenormally closed contacts Aar. The energizing of relay F4 closes contactsF115, F175, F05 completing the three phase power circuit to the motor 46for operating it to close the finishing valve 28. It also completes alocking in circuit by the closing of contacts F114. When the finishingvalve 28' has closed, torque limit switch contacts Aa4 open breaking thecircuit through relay F4 and permitting contacts F115, F195, F04 to openstopping the motor 46. This action also closes normally open contactsAbs of the torque limit switch in the sequence circuit.

Open roughing valve.

The next step is to open the roughing valve 23. Since the roughing valveis closed, limit switch contacts Bba are open, and relay R3 is deenergized. Contacts Rag are normally closed when relay winding R: isde-energized. As contacts Abs have been closed as previously indicated,a circuit through closed contacts Bus and the coil of relay Y3 iscompleted and the winding of that relay is energized so that contactsYa. in the opening control circuit of the roughing valve 28 are closed.When the pressure in the header is below microns at the start of thesequence operation, relay C3, controlled by the Pirani pressure gauge ina manner heretofore described, remains de-energi'zed by the action ofrelay 0-.1 in opening the contacts 0]3, permitting contacts Cd; in theopening control circuit of roughing valve to remain closed. Sincecontacts Gar are closed by energizing relay G4 in response to theclosing of the main gate valves 24, 25 and through relay contacts M114and MMb4 as heretofore described, a circuit is completed through coil ofrelay VV4 locking itself in by closing contacts VVd4 and closingcontacts VVas,

V'Vbs, VVc5 for connecting the motor 41 of roughing valve 23 to thepower supply for driving the roughing valve to open position. Whenroughing valve 23 opens, normally closed torque limit switch contactsB114 are driven to open position breaking the circuit through winding ofrelay VV4 and permitting contacts Was, VVb5 and VVc5 as well as'holdingcontacts VVd4 to open removing the power from the motor and. opening airto enter the vacuum pump, the Pirani sys-- tem acts in a mannerhereinbefore described, to de-energize relay O2, permitting contacts 0]:to close energizing relay C3 which seals in through contacts Ca; andopens contacts Cd; in the opening control circuit for the roughingvalve, thus preventing subsequent opening of the roughing valve 23 bymotor 41 during the sequence when pressure may reach a level below 100microns. By the same operation, contacts CD3 and C04 are closed.

Closing roughing valve The next step in the sequence is the closing ofthe roughing valve 23, after the mechanical pump has completed theroughing operation.

With the contacts Rb-i closed as previously described, the pressurehaving reached a point below 100 microns, the Pirani control systemoperates as hereinbefore described to energize relay 02, open contactsOh and close contacts 003 to complete the circuit to relay winding Q3energizing it and closing contacts Qas in the closing control circuitfor the roughing valve. This completes the circuit through relay windingV4. When winding V4 is energized, contacts V115, Vb5, Vcs are closedcompleting the power circuit to the driving motor 41 for the roughingvalve 23, causing it to drive the valve to closed position. This sameaction closes contacts V034 creating a holding circuit for the relayWinding V4. When roughing valve 23 has closed, torque limit switch openscontacts Sal breaking the circuit through the relay winding V4 andopening contacts Va5, Vbs, V05 removing the power from the motor 41. Thetorque, limit switch also closes contacts $193 in the sequence circuit,completing the circuit through normally closed contacts U03, andenergizing relay winding W3 which closes contacts The next, step is theopening of the finishing valve 28. When the pressure rose and relay 02was de-energized as heretofore described in connection with the Piranicontrol circuits, relay Cs was energized. This took place when theroughing valve 23 was opened and the pressure rose, so that contacts C6;in the opening control circuit for the motor 46 of the finishing valve.28 are closed, and the closing of locking in contacts Caz keep relay C3energized while relay O2 is still energized; Likewise, the energizing ofrelay W3 through action of the torque limiting switch upon the closingof roughing valve 23 and closing of the contacts W614 in the openingcontrol circuit for finishing valve 28 as described above completes thecircuit through coil of relay FFi.

This closes a locking-in circuit through contacts FFd4, and also closescontacts FFas. FFb5, FFCs completing the power circuit to the motor 46for opening finishing valve 28. When finishing valve 28 has opened,torque limiting switch opens contacts E614 and breaks the circuitthrough relay FE; de-energizing that relay and permitting contactsFFCts, FFbs, FFCs to open, breaking the power circuit to the motor 46driving finishing valve 28. The opening of the finishing valve acts toclose contacts. Eba of the torque limiting switch, energizing relay U3.It may also permit the pressure in the vacuum chamber to rise above 100microns when communication is established with vacuum pumps [9, 20.

Opening main gate valves The last step in the sequence is the opening ofthe main gate valves. The energizing of relay U3 described above closescontacts Uas and U64 in the opening control circuits for the main gateValves. When the pressure drops below microns, or if it has remainedbelow that level, relay O2 is energized as describedhereinbefore inconnection with the Pirani system. Contacts 003 are closed and relay Q3is energized. Contacts Qbi and Q04 are closed, and since contacts Mb4and MMbi are also closed when gate valves 24, 25 are closed, relay G4 isenergized and contacts Gds and Gel are closed completing circuitsthrough the opening control circuit for the main gate valves 2 25 toenergize coils H4, I4. They close contacts Has, Hbs. H05 and Ice and lbsand I05 to operate the driving motors 44, 45 for the main gate valves24, 25 to the power supply moving the main gate valves to open position,in addition they close locking in contacts Hdi and Ids, respcctively.When main gate valves 24, 25 start to open. limit switches Mbi and MMb4are opened (lo-energizing relay G4. This opens contacts Gbs whichde-energizes relay K3 and opens contacts Kba which in turn opens thesequence circuit and permits contacts Kfs to close which lights sequencecompleted lamp 88 through transformer 89. It also opens contacts Gal inthe opening control circuit for the motor 4'! of roughing valve 23.preventing accidental operation thereof. When main gate valves 24. 25have opened gear limit switches Pan and Tai open de-energizing relays H4and I4, respectively, re-opening the power circuits to the operatingmotors 44, 45 for valves 24, 25 and stopping them. This completes thesequence.

When contacts IVHM and MMb open at the finish of the sequence, relay G4is de-energized closing contacts Gcz which were open during the sequenceoperation. Since during the operation of the sequence the pressure roseabove 100 microps. coil. BB2 was at one time energized closing contactsRRb2. This action energized QQZ which sealed itself in through QQaz andclosed contacts QQZJZ. Thus when contacts Gog close as described above.energy is supplied to the bell which rings signalling the end of thesequence operations. The hell, can be silenced as indicatedhereinbefore.

If at any time it is desirable to stop the seouence circuit, it can bedone by merely depressing button 55 (sequence stop) located in thesequence circuit. which de-energizes relay K3 and opens contacts K173and K514. This disables the sequence circuit. de-energizes relay N andreturns all of the valve operation circuits to manual operation throughmanual switches is to 55, inclusive, by the closing of contacts No.4,Nbi, N04, Ndl, N84, Nfi.

If desired. pilot lights Bil, BI, 82, 93, 94, 95. 96, and 9! may beconnected to the various opening and closing control circuits of thevalves 24, 25, 25' and 23 through a propriate coupling transformers 98.99. Hill. IM. H32, H33, H94 and its to indicate the operation of thesevarious circuits.

It will also be understood that line [08 of the power circuit isconnected to and feeds line H11, and that lines H39 and I H! areconnected together. Rwitches l i l l [2 serve to complete the circuit tothe main power line H3 which furnishes power at conventional voltagesand frequency.

Having thus described my invention, I claim:

1. A system for evacuating a chamber comprising a mechanical pump andplurality of diffusion pumps, valve means connecting each of said p psto the chamber and to each other, means responsive to pressures above apredetermined value for operating said valve means to connect themechanical pump with the chamber to partially evacuate it, and meansresponsive to pressures below the predetermined Value for operating thevalve means to connect the mechanical pump in series with the difiusionpumps to receive their outputs and evacuate the chamber to a high vacu-2. A control system of the character described comprising a chamber, alow vacuum mechanical pump, high vacuum diffusion pumps, valves forconnecting the diffusion pumps to the chamber, a finishing valve forconnecting the mechanical pump to the diffusion pumps, a by-pass linefor connecting said mechanical pump to said chamber for roughing downpurposes, a roughing valve in said by-pass line, means responsive to apredetermined pressure in the system for controlling the opening of theroughing valve to connect said mechanical pump with the chamber andpartially evacuate it, and means responsive to a predetermined lowerpressure for closing the roughing valve and opening the other valves toplace the mechanical pump in series with the diffusion pumps andevacuate the chamber to a low pressure.

3. A vacuum system of the character described comprising a chamber,mechanical and diffusion pumps for evacuating the chamber, valves forconnecting the diffusion pumps to the chamber,

a finishing valve and a roughing valve for connecting the mechanicalpump to the diffusion pump and to the chamber through a common inlet, acircuit for selectively actuating said first named valves, saidfinishing valve, and said roughing valve, and pressure responsive meansin communication with said common inlet, said pressure means beingresponsive to predetermined changes in pressure for controlling theoperation of said circuit to open and close the roughing valve in timerelation to the opening of the other valves to connect the mechanicalpump, and then the diffusion and mechanical pumps in series to saidchamber and eifect partial and substantially complete evacuation of thechamber.

4. A control system of the character described comprising a chamber tobe evacuated, a high vacuum and a low vacuum pump, valve means forconnecting said high vacuum pump and said low vacuum pump to the chamberin a predetermined sequence for evacuating the chamber, said meansincluding a circuit responsive to pressure conditions in said chamber, asequence circuit coupled to and responsive to the action of the circuitfor determining the sequence of coupling of the high vacuum pump and thelow vacuum pump to said chamber, and a power control circuit coupled toand responsive to said sequence circuit for carrying out the couplingsequence of the low vacuum pump and the high vacuum pump to said chamberin a predetermined manner.

5. A control system of the character described comprising a chamber, ahigh vacuum pump and a low vacuum'pump, valve means for coupling saidhigh vacuum pump to said chamber and said low' vacuum pump to saidchamber and said high vacuum pump, a pressure device responsive topressure conditions in the system, a signal circuit coupled to andcontrolled by said pressure device, a sequence circuit coupled to andcontrolled by the signal circuit for determining the order of o erationof the low vacuum pump and the high vacuum pumps in the system, and apower control circuit responsive to the action of the sequence circuitfor altering the coupling of the high vacuum pump and low vacuum pump inthe system.

6. A control system of the character described comprising a chamber, ahigh vacuum pump and a low vacuum pump, valve means for coupling the lowvacuum pump to the chamber and to the output of the high vacuum pump,valve means for coupling the high vacuum pump to said chamber, means forcontrolling the action of said first and said second coupling meansincluding a pressure controlled circuit responsiveto pressure conditionsin the system, a sequence circuit coupled to and activated by thepressure controlled circuit for determining the order of coupling of thelow vacuum pump and the high vacuum pump to the chamber and to eachother, and a power circuit coupled to and energized in response to theaction of the sequence circuit to actuate the coupling means for the lowvacuum pump in a predetermined manner and the high vacuum pump.

7. A control system of the character described comprising a chamber tobe evacuated, a low vacuum pump and a high vacuum pump, means forcontrolling the order of coupling of the low vacuum pump and the highvacuum pump to the chamber and to each other, said means including apressure responsive circuit responsive to predetermined pressureconditions within the system, a signal circuit mechanically coupled tosaid pressure responsive circuit and energized in response thereto, asequence circuit coupled to and electrically controlled by the signalcircuit for determining the coupling arrangement of the said low vacuumpump and the high vacuum pump at predetermined pressures, and a powercontrol circuit activated by said sequence circuit to bring the lowvacuum pump and the high vacuum pump into coupling relation in apredetermined manner. 1

8. A vacuum control system of the character described comprising achamber, a low vacuum pump and a high vacuum pump, means for bringingthe low vacuum pump and the high vacuum pump into communication withsaid chamber, a signal circuit, pressure responsive means coupled to thesignal circuit for controlling its operation, a sequence circuit coupledto and operated by signals from said signal circuit, power controlcircuits connected to and responsive to the operation of said sequencecircuit to actuate said communicating means and connect the low vacuumpump and high vacuum pump to said chamber in a predetermined sequence toexhaust said chamber to a high vacuum.

ROB ROY CYR.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,716,160 Zworykin et a1 June 4, 1929 2,063,665 Edwards Dec.8, 1936 FOREIGN PATENTS Number Country Date 203,702 Great Britain Jan.10, 1924

